Evenin'
After my regular check-over of fluid levels a few days ago I found my battery needed topping up. It's been performing fine, but took about half a litre.
After a brief drive this morning I noticed the breather was overflowing by a small amount. Infact I smelt it before I saw it. Thought initially this was just down to my overfilling the cells. Just got back in this evening and it's still dripping, and also a slight trace of steam? I've done about three hundred and fifty miles or so today. Can any possible overfill still be escaping after such a distance - or is it time for replacement?
Simon
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Simon,
It might be worthwhile checking the battery voltage while the engine is running (and revving at ~3000rpm) to make sure the battery isn't being overcharged by the alternator.
Number_Cruncher
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Thanks, I've got a multimeter here. Presumably it should be reading around 12v?
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Thanks, I've got a multimeter here. Presumably it should be reading around 12v?
Assuming 12 volt electrics, fully charged battery with the alternator running should be near 14.7 volts.
Higher than that is a problem.
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As NC said,though it is usually alternator overcharging and can destroy the battery
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Steve
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If your meter can read amps on a 10 amp range. Wait until the you know the baerry is at max charge i.e. run the engine for 10 mins then get another pair of hands to hold the meter probes one on the Lug and one on the terminal then carefully disconnect the positive terminal just enough the the meter reads. If this is 5 or maore amps then the alternator regulator has probably failed. this should have shown up on the voltage check , if it read 15.75v plus then the reg is away. The only other possibility is one cell is failing or a liml ber internally and the high resistance is heating up and boiling the electrolyte. Is the whole battery getting warm or just one part. Regards Peter
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Thanks,
Will try reading the amps tomorrow.
Quick check just now couldn't get it to read more than 14.10v when revving around 3,000rpm.
Of the six cells, the ones at each end (i.e. nearest terminals) are cooler than the two in the middle. These are hot - almost too hot to touch.
Simon
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Simon,
It sounds like Peter D's suggestion of a duff cell, shorting out, in the battery is the problem, although checking that the alternator current drops off correctly will rule out the alternator completely.
Number_Cruncher
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WARNING WARNING If the cells are that hot you are in fact overcharging BEWARE the fumes given off are an explosive mis of Hydrogen and Oxygen so be very casreful when you do the current check. I would place a fan heater near by just blowing cold air over the battery to avoid the possibility of you causing a spark with the current test and igniting the fumes. It's a nice clean burn though, no smoke except for patting your fringe and eyebrows to put them out. No to be seriuos there is a risk of the fumes igniting in the battery and it blowing the top off. Take care. Regards Peter
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Morning,
I'd be disappointed if it was the alternator/regulator that was at fault as it was replaced about a year ago.
That statement has just got me thinking - I remember it being said at time of fitting that the replacement item was of a slightly higher rating than the original. The battery on the vehicle is 88Ah. I just checked with dealer who says they are now all 100Ah. Could the replacement alternator's higher output have contributed to the problem?
Also, the current test: is that performed with the engine running or off?
Thanks,
Simon.
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No the battery ampage is not a concern and the test is done after 10 minutes running and at 2500 rpm. Regards Peter
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Quick check just now couldn't get it to read more than 14.10v when revving around 3,000rpm. Of the six cells, the ones at each end (i.e. nearest terminals) are cooler than the two in the middle. These are hot - almost too hot to touch.
Sounds like a faulty battery, as the 14.1v is okay for alternator voltage. Usually when the alternator develops a faulty regulator, the voltage just rises and rises as the engine is revved, leading to the battery 'boiling'and giving off an acid mist when it gets realy bad.
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The voltage is of no great concern at around 14V its the ampage output that is important ,you yourself has said they have fitted a high output alternator so in effect you are frying the battery.This can be extremely dangerous and you should not be driving the vehicle for your safety and others around the vehicle when it blows up and I do see your insurance paying up.
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The replacement alternator is rated at 90Ah, and I think the original was 80Ah. The battery was 88Ah, so still compatible on the face of things, although I freely admit I'm not knowledgeable on the subject.
This morning I've swapped that battery for a new 100Ah - main dealer was same price as local auto-electrical supplier.
The original battery's done well I think: five years, 330,000 miles.
Thanks for all your advice and suggestions everyone.
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An alternator rating is designed to the maximum demand of all the electrical loads of the vehicle and leave a few amps 3 of 4 to keep the battery floated at about 14.4 to 14.75 volts tops. the excess power of the alternator is not just dumped into the battery. Keep an eye or hand should I say, on the new battery temp and if it remains cool then fine, but beware and take care. Regards Peter
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An alternator rating is designed to the maximum demand of all the electrical loads of the vehicle and leave a few amps 3 of 4 to keep the battery floated at about 14.4 to 14.75 volts tops. the excess power of the alternator is not just dumped into the battery. Keep an eye or hand should I say, on the new battery temp and if it remains cool then fine, but beware and take care. Regards Peter
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Absolutely right, the fact you have a heavy-duty alternator should make no difference 'amp-wise', as it is the batterys internal resistance which governs whether a ton of current flows in or not. All a heavy duty alternator does for you is to allow extra wattage for additional devices whilst still maintaining normal levels of charge to the battery if needed. In esscence you could put a 150amp alternator on a car which normally has a 60amp alternator and it should make no difference to the battery charging, as the maximum charge voltage would be pegged at say 14.7v, meaning that the current would equal the voltage divided by the battery resistance at any time.
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